Gas fired infrared dryers and hot air dryers have been used successfully for many substrate drying and curing requirements for many years. Combinations of the two methods have also been utilized with some success. In these practices a substrate, which is usually a sheet of paper, is moved in proximity to the dryer so as to be subjected to a heated flow, such as from heated air, to dry the substrate and any coating on the substrate. Conventional air dryers are often started thirty or more minutes before start up because of thermal lag. This results in detrimental down time which could be quite costly, particularly over a long period of time.
An object of this invention is to provide an infrared and hot air dryer combination which utilizes the many advantages of an advanced IR (infrared) emitter to provide the best combination of the two technologies of gas fired infrared dryers and hot air dryers.
In accordance with this invention an IR emitter is provided which includes a pressurized hood having a series of gas infrared emitters mounted at the bottom of the hood disposed toward the path of flow of the moving substrate or paper sheet. The hood has an air inlet delivery duct attached at one or both ends and includes a mixer for each cross-direction zone. Gas is supplied to a header in the hood and then to each mixer to create a gas/air mixture which is fed to the infrared emitters. An exhaust chamber is mounted to and downstream from the hood. Air conveying tubes made of thin wall material extend from the hood into the exhaust chamber in a non-linear path which functions as a heat exchanger to quickly heat the air passing through the tubes. The tubes communicate with air bars downstream from the IR emitter to further dry the paper sheet.